1. Technical Field
The present invention relates to wireless communications and, more particularly, to integrated circuit radio frequency synthesizer circuitry for providing low noise and low power consumption frequency control.
2. Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards, including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of a plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via a public switch telephone network (PSTN), via the Internet, and/or via some other wide area network.
Each wireless communication device includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier stage. The data modulation stage converts raw data into baseband signals in accordance with the particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier stage amplifies the RF signals prior to transmission via an antenna.
Typically, the data modulation stage is implemented on a baseband processor chip, while the intermediate frequency (IF) stages and power amplifier stage are implemented on a separate radio processor chip. Historically, radio integrated circuits have been designed using bi-polar circuitry, allowing for large signal swings and linear transmitter component behavior. Therefore, many legacy baseband processors employ analog interfaces that communicate analog signals to and from the radio processor.
Within an integrated circuit radio transceiver, a precise signal frequency is required for conversion to and from radio frequencies. Traditional circuits, and more particularly, loop filters in phase locked loop (PLL) applications, are known to be noisy, require a certain amount of power, and consume valuable hardware resources.
FIG. 1 is a block diagram of a prior art phase locked loop that includes a traditional loop filter for generating an input signal to a voltage controlled oscillator. In general, a phase frequency detector (PFD) is operable to generate a pair of control signals to a corresponding pair of current sources that are configured to operate as a current source and as a current sink. Typically, such a configuration requires the sources to be matched in functional capability so that equivalent control commands to source or to sink current will have equivalent effects. Thus, as may be seen, the two current sources are operably disposed on different sides of a node that sources or sinks current to a loop filter. Thus, if no change to the voltage controlled oscillator (VCO) output frequency is required, meaning no change is required to the signal level produced to the VCO, then it is desirable for the current source coupled downstream of the input node to the loop filter to sink the exact amount of current produced by the current source upstream of the input node to the loop filter. By matching the current generated by both current sources, the signal level generated by the loop filter to the VCO remains constant and the VCO produces a constant frequency output.
As may further be seen, the traditional loop filter of the PLL of FIG. 1 includes series coupling a capacitor and a resistor that which are jointly are in parallel to a capacitor. Further, both capacitors are coupled to circuit common. In general, when current is sourced into the loop filter, the charge on the capacitors increases thereby increasing a direct current (DC) voltage signal level produced to the VCO and, therefore, the output frequency of the VCO. When current is sinked from the input node to the loop filter, the charge and VCO input signal level are decreased thereby decreasing the VCO output frequency. Thus, the PFD is operable to control the output frequency of the VCO by generating control commands to switches between the input node to the traditional loop filter and each of the two current sources to control relative sourcing and sinking of current to or from, respectively, the input node to the loop filter. Thus, the PFD controls the VCO output frequency by sourcing net current into, sinking net current from or maintaining an equal amount of current sourced and sinked from the input node to the loop filter. Typically, for noise purposes, the capacitors of the loop filter and the current sources are relatively large to reduce noise to reduce interference with RF signals being processed by frequencies generated by the loop filter.